This project is a continuation of our ongoing investigation of the relationships between androgen and male sexual behavior. An extensive study will be conducted on the androgen-dependence of two components of the total behavior pattern: sexual reflexes; and sexual arousal in the absence of gonadal input. Particular attention will be paid to androgenic control of erection. Radioimmunoassay of testosterone will be used to determine androgen levels in animals treated with constant release (Silastic) capsules, and dose-response curves derived for the various functions in young and aging adults. We will attempt to define the nature of the declining sexual capacity in old age and to determine the possible involvement of decreasing androgen levels therein. A major objective will be to distinquish the respective roles of androgen and non-androgen dependent central versus peripheral mechanisms in male sex behavior, by using techniques of lesioning and steroid implantation in brains and administering steroids and antiandrogens which have selective effects on genital morphology and/or sexual behavior. Additional studies will be performed to investigate correlations between circulating androgen and socio-sexual behavior in a seasonally breeding primate, the squirrel monkey.